When subjecting metal objects to heat treatment in a continuous operation, such as sheet-iron strip for instance, it is common practice to use as support for the material under treatment, at the openings of the furnaces, and if necessary, between furnaces, roller sets in which two alternatingly operating rollers have been placed side by side. It is then possible to lift each roller by itself into operating position or to lower it into the changing position. A drawback is the great height required in the openings of the furnaces, because the sag of the strip's catenarian curve is different according to whether the roller doing the supporting is that closer to the opening or that lying farther away. It is also a fact that the strip between furnaces cools, and sealing of the openings is difficult, whereby considerable energy losses are incurred.
For supporting the material in continuous-action heat treatment furnaces there has also been used a water-cooled support roller set pushable into the furnace through its side. In this case, the support roller set is in the hot furnace throughout the operating time, whereby its service life is significantly curtailed. In addition, the replacing of a single roller is inconvenient, and the material is highly susceptible to scoring. Furthermore, sealing of the opening of the furnace is difficult.